1. Field of the Invention
The invention relates to an optical data-projection device that projects data such as the date onto photographic film.
2. Description of the Related Art
Conventional data-projection devices for use in cameras typically include a liquid crystal panel capable of displaying data such as date and time and, define a light path for guiding light emanating from a light source through this liquid crystal panel. The light filtered by the LCD is then displayed on this liquid crystal panel and is projected onto photographic film contained within the camera during exposure. In the most common arrangement, the data-projection device is installed on the back lid of the camera so as to face the back side of the film mounted in the camera, and uses a light source such as a lamp to project data onto a specific area (several millimeters) on the back side of the film.
By contrast, other configurations are proposed such as that disclosed in Japanese patent application No. S56-139141 which uses the externally generated light such as sunlight. FIG. 18 schematically shows the configuration of this camera. Photographing shutter 8 is positioned between camera photographing lens 6 and photographic film 16, and an image is projected onto area 13 of film 16 when shutter 8 opens. In addition to this optical system, transmission-type projection liquid crystal display device 3 which is capable of forming the data pattern to be projected onto the photographic film, is positioned between external light intake area 76 and photographic film 16. Therefore, after filtering by projection liquid crystal display device 3, external light 77 taken in from external light intake area 76 exposes photographic film 16 via data lens 9 and projects a data image corresponding to the data pattern onto area 12 of photographic film 16. This data-projection operation is controlled by photographing shutter 8 and occurs in synchronism with a normal photographing operation.
The above-described configuration results in lower manufacturing and parts costs because the data-projection device need not include an internal light source, and there is no need for a separate trigger signal generation device for data projection because the shutter of the camera is used as a projection trigger. This configuration also offers an advantage because the use of external light for projection results in a constant brightness ratio between the photographic object and the data to be projected, resulting in a constant photographic density of the projected data and making it possible to clearly project the data even in a camera lacking exposure correction. Therefore, this configuration is suitable to applications such as disposable cameras for which low cost is a prime concern.
However, the following problems exist when using the conventional ambient light driven data-projection device described hereinabove. When affixed to a disposable camera, such a data-projection device is positioned in the front part of the camera. Consequently, space cannot be allocated for a display device for monitoring the data to be projected because the front face must also accommodate a photographing lens and a shutter. Therefore, one conventional design trend is to reduce the size of the data-projection window and limit the data to be projected to year, month, and date only, by not offering data selection or correction, and by eliminating the typical mode selection/correction switch and the display device for monitoring. However, the lack of a monitor display and a correction switch makes it impossible to check for or correct faulty projection data, which can be caused by external noise such as static electricity and the impact of being dropped. And, particularly in the case of a disposable camera, the noise from the strobe circuit board during strobe charging or discharging can cause an error or malfunction when the data-projection device is positioned proximate the strobe circuit board.
It would be desirable if a function for checking data could be provided without the installation of a dedicated display device for monitoring. Accordingly, Japanese patent application No. S56-101135 discloses a known data confirmation method using ambient light in which a reflection mirror is installed on the top surface of a shutter located on the back of a projection liquid crystal display device so that display contents can be checked. A problem remains in this case, however, in that the data image viewed is inverted, thereby making confirmation difficult. Although it is possible to electrically invert the display, the font is predetermined and thus simple inversion will not make the confirmation of the projected data any easier.